We propose to develop a zone plate based, multi-keV x-ray imaging facility at the Stanford Synchrotron Radiation Laboratory (SSRL) that will be capable of imaging thick hydrated biological specimens with 20 nm resolution and provide three dimensional images using tomographic reconstruction. By using x-ray phase contrast imaging as well as contrasting agents and specific labels such as immunogold, quantum dots, or other labeling techniques developed for electron microscopy, the instrument will be a tool for mapping specific molecules in cells or cells in tissues. With the anticipated improvements in zone plate optics, we expect the resolution to ultimately reach or exceed 10 rim. This instrument is meant to be used by the biomedical research community at large, and therefore in its construction we will demonstrate its efficacy on two radically different biological problems: (1) mapping microbes and macromolecules in wound tissue and (2) determining the nanostructure of hydrated bone. This proposal combines the expertise of three collaborating organizations: Prof. P. Pianetta and Dr. K. Luening from SSRL with extensive experience in a wide range of x-ray techniques based on synchrotron radiation sources; Dr. E. Almeida (UCSF, NASA Ames Research Center) and Prof. M. van der Meulen (Cornell University) who are leaders in studies of the nanostructure of bone; and Dr. J. Trent (NASA Ames Research Center), an accomplished microbiologist, who has worked extensively in imaging microbes and macromolecules and currently heads a research team studying the microbial ecology of chronic wounds. The microscope will be purchased from Xradia Inc., a leader in developing nondestructive high-resolution x-ray imaging solutions using multi-keV x-rays produced by a laboratory x-ray source. Dr. Wenbing Yun, founder and president of Xradia, will serve as a consultant on the project to develop the techniques needed for achieving high resolution 2D and 3D images in phase contrast for real biological specimens.